This application relates to and claims priority, under 35 U.S.C. xc2xa7 119, from French Patent Application No. 99 07313, filed on Jun. 10, 1999, the entire contents of which are hereby incorporated by reference herein.
1. Field of the Invention
The present invention generally relates to turbojet engines including inlet guide-waves having vanes at an angle which is controlled during operation of the turbojet engines and more particularly, to a protection device for protecting the control mechanism or control actuator which controls an orientation of the angle of the vanes.
2. Discussion of Background
When certain turbojet engines are used, such as those used in fighter planes, certain flying conditions impose stresses on the airflow at the turbojet engine intake. Indeed, under specific meteorological conditions and for given operating conditions of the turbojet engine phenomena occur that disturb the airflow at the turbojet engine intake, such as xe2x80x9csurgingxe2x80x9d. Phenomena of this kind mean that the actual instantaneous airflow at the turbojet engine intake is different from the theoretical airflow required at that particular instant for the preferred operating conditions of the turbojet engine. Phenomena of intense and violent aspirations then occur at the inlet guidevanes of the turbojet engine, particularly at its orientable vanes. This results in aerodynamic instability in the compressor.
Similarly, when the plane is stopped or flying at very low altitude the ingestion of objects or flying objects can cause major impact to one or more vanes. It then causes damage to or breaks one of the parts constituting the mechanical chain of the vanes. However, in most turbojet engines the mechanism chain is controlled by an actuator that operates with the fuel of the turbojet engine under pressure. Such an impact to one of the vanes could cause damage to the control actuator and a major fuel leak, either directly or indirectly due to one of the parts of the mechanism chain. Such an occurrence should be prevented in any event to avoid endangering any flight that uses one of these turbojet engines.
The aim of the invention is therefore to ensure flight safety of planes that use turbojet engines of this kind by protecting the fragile parts, such as the vane control actuator of the inlet guide-vanes.
Besides, U.S. Pat. No. 4,695,220 discloses a frangible mechanism system that limits the loads on each vane of the inlet guide-vanes of a turbojet engine in the event of foreign bodies being ingested. Each vane is fitted with a frangible part between the control lever and the inlet guide-vane control ring, which protects each vane when it is subjected to an impact. Once the frangible part has broken, the indentation in the ring limits the displacement of the vane control lever. Various damping systems are used, such as springs and elastomer materials, in the indentation of the ring to absorb the impact when the frangible part breaks.
The drawback of this type of solution is that it requires every vane to be fitted with a frangible part, which is a disadvantage in terms of construction, light and cost.
To overcome the above-described drawback, the main aim of the present invention is a protection device for protecting the control mechanism of the inlet guide-vanes at the entrance to a turbojet engine. The protection device comprises: a control actuator; a frangible transmission part activated by the control actuator; a control ring driven by the control actuator by means of the frangible transmission part; and a control lever for directing each of the inlet-guide vanes, wherein each control lever is activated by the control ring.
According to the present invention, the frangible transmission part is a single component and constitutes a link in the control mechanism positioned between the control actuator and the control ring.
In a preferred embodiment of the present invention, the frangible transmission part is a connecting rod. The connecting rod has a portion with a narrowed cross-section which is located between the control actuator and the control ring. Only one pivoting transmission part is used at the outlet of the actuator and the one pivoting transmission part is located before the connecting rod and is articulated around the actuator and the connecting rod.
In this case, it is advantageous to provide a protective part which is tubular so as to surround the portion of the connecting rod having the narrowed cross-section. This tubular protective part can advantageously take the form of a double-thickness thermoshrinkable sheath.
Also, the narrowed cross-section portion and the remainder of the connecting rod may be tube-shaped.
In another embodiment of the present invention, the frangible transmission part is a frangible bolt having a narrowed cross-section portion that is positioned in a yoke downstream of the pivoting transmission part.
In order to prevent the connecting rod, once broken, from damaging a mechanical part of the mechanism, particularly the actuator, it is very advantageous to fit an anti-deflection part to a downstream yoke of the pivoting transmission part and to cover the end of the connecting rod to prevent the connecting part from rotating at such an amplitude as to subject the actuator to an impact.